Samsung j2 is a smartless phone. Basic problem is nerwork signa2 and changing nerwork automatically from 2G to 3G ro 4G based on available network on that area.This problem will not be noticed by people who are always in 3G area. Those who are travelling has several problem where phone will not be reachable once there is change in network. Even service center cant eesolve this issue. I got 2 times phone replaced but still same problem . I cant replicate this problem in service center because there is no change in network. But problem when travelling outside